This application requests funding for the study coordination, data management, and biostatistical support for a Phase III clinical trial of Coenzyme Qio (CoQ) in Huntington's disease (HD). This is a companion application to that of Merit E. Cudkowicz, M.D. from Massachusetts General Hospital entitled "Coenzyme Qio in Huntington's Disease (2CARE)." The primary aim of the project is to conduct a multicenter randomized, double-blind, placebo-controlled trial of CoQ at a dosage of 2400 mg/day involving 1100 ambulatory subjects with HD followed prospectively for five years. CoQ is a cofactor involved in mitochondrial electron transfer and an antioxidant that has demonstrated increased survival in a transgenic mouse model of HD and promising results in human trials in HD and Parkinson's disease. It is hypothesized that chronic treatment with high-dosage CoQ will slow the progressive functional decline in HD. The specific aims of our application are (1) To provide project coordination for the trial including: development and implementation of web-based randomization and enrollment procedures, provision of study documents (protocol, model consent and assent forms, operations manual, case report forms), training of site personnel and standardization of study procedures, facilitation of recruitment and retention of a diverse sample of research subjects, and packaging and distribution of study drug; (2) To provide data management for the trial including:receipt and entry of all data in a relational database, generation and resolution of data queries, monitoring of important study events, and maintenance of a compliant and secure data environment; and (3) To provide biostatistical support for the trial including: refinement and implementation of the statistical analysis plan to address the specific aims of the trial; design and implementation of an interim monitoring plan that will allow modification or termination of the study on the basis of early evidence of either (i) safety concerns, (ii) overwhelming evidence of efficacy, or (iii) futility, in conjunction with the NINDS-appointed Data and Safety Monitoring Board (DSMB); and preparation of open- and closed-session reports for the DSMB.